The post office makes money from delivering packages for Amazon and other companies. In 2019, they made $1.6 billion delivering packages just for Amazon alone. We have known this for some time. It proves that Trump is lying as usual and his diatribes against delivering packages for Amazon stem from his desire to attack his perceived political enemies.
It also proves something else. Trump is a rotten businessman. The Post Office is a consumer driven business and that is something that Trump has consistently failed at. The Post Office should be making capital investments such as sorting machines for packages and trucks that can hold more packages. This would assist the post office in making the part of their business that is growing more profitable.